The mechanisms of tissue injury and cell death is unknown. However, maintenance of membrane integrity, particularly of lysosmal membranes, is essential to preserve the structural and functional properties of cells. This proposal examines the contribution of membrane lytic enzymes (phospholipases A, PLA) to 1) the initiation and potentiation of tissue damage during pulmonary ischemia and 2) the bacteriolytic system of lung. At various times after obstruction of the blood supply of isolated, perfused rabbit and dog lungs, PLA activity toward synthetic substrates will be determined in subcellular fractions of normal and ischemic lung. Endogenous phospholipid hydrolysis will be monitored by quantitative thin layer and gas liquid chromatography and morphologic alterations by electronmicroscopy. We wish to determine: 1) the cellular and subcellular localization of PLAs active during ischemia, 2) if PLAs function to initiate membrane damage in pulmonary cell lysosomes subsequently releasing tissue-destructive acid hydrolases, and 3) if highly purified alveolar macrophage PLA, like the leukocyte enzyme, has potent bactericidal activity. Granules derived from pure cell types, alveolar macrophages and polymorphonuclear leukocytes, with well defined PLAs will serve as models to examine lysosomal PLA activation, membrane damage and lysosomal enzyme release. Physiologic factors and pharmacological agents that modulate lysosomal PLA activity will be studied. With a focus on the ischemic lung, it is hoped that this approach will lead to a better understanding of the relationship between membrane structure and function, and the role of phospholipase A-induced membrane perturbations in tissue injury.